The present invention provides a procedure for manufacture of dimethylsulfoxide by oxidation of dimethylsulfide by means of hydrogen peroxide.
Several methods have been proposed to accomplish the oxidation of organic sulfides to corresponding sulfoxides. Industrially, for example, dimethylsulfoxide is made by oxidizing of dimethylsulfide with oxygen in the presence of nitrogen dioxide (Kirk-Othmer, Encyclopedia of Chemical Technology, 3d Ed., Vol. 19, pages 332 and 333). This procedure involves a number of deficiencies, however. It is specially dangerous in that mixtures of dimethylsulfide and oxygen are explosive over a wide range of composition. It is difficult to stop the oxidation at the dimethylsulfoxide level and greater than negligible quantities of dimethylsulfone are formed which must subsequently be separated. Furthermore, the crude dimethylsulfoxide is very acid and must be neutralized before being dried and distilled.
Other agents for oxidizing dimethylsulfide indicated in the literature include hydrogen peroxide, ozone and organic hydroperoxides.
In regard to oxidation by hydrogen peroxide, the prior procedures involve various disadvantages such as the necessity to work at low temperature and to use special apparatus, the critical dependence on pH and, above all, the obtainment of a dimethylsulfoxide containing more than its weight of water.
Russian patent No. 165,713, for example, describes the oxidation of dimethylsulfide by 30 percent hydrogen peroxide by bubbling dimethylsulfide vapor mixed with a gas, such as air, through the peroxide solution at 50.degree. C. in an apparatus having five oxidation columns.
In Russian patent No. 175,055 the dimethylsulfide is preliminarily treated with sufficient cuprammonium solution to obtain a pH .gtoreq. 8, and then is mixed under very rapid agitation (6000 rpm) with 30 percent aqueous hydrogen peroxide at a temperature not exceeding 20.degree. C.
In Russian patent No. 249,375 dimethylsulfide is treated with sulfuric acid until the concentration of sulfur dioxide in dimethylsulfide reaches 4 to 11 grams/liter, before then oxidizing with 30 percent aqueous hydrogen peroxide.